1. Technical Field
The present invention relates to airbag inflators. More specifically, the present invention is a new type of airbag dual-stage inflator that may be used with vehicle airbag systems.
2. Description of the Prior Art
Vehicle airbag systems are known in the art and have been credited with greatly increasing the overall safety of motor vehicles. Specifically, these airbag systems are designed such that during an accident, one or more airbags will be rapidly inflated and will be positioned between the vehicle occupant and the hard surfaces of the vehicle interior. These inflated airbags will inhibit the vehicle occupant from impacting the interior surfaces of the vehicle and will thus greatly reduce the likelihood that the occupant will experience significant injuries in the crash.
As is known in the art, airbag systems will generally include an inflator that is capable of rapidly producing a large quantity of gas. As its name implies, the purpose of the inflator is to “inflate” the airbag. When an accident occurs, the inflator will rapidly produce a large quantity of gas that is then channeled into the airbag. In turn, such rapid influx of gas inflates and expands the airbag and causes the airbag to become positioned in front of one or more of the interior surfaces of the vehicle. As accidents occur quickly, this inflation of the airbag must occur very rapidly-i.e., generally within approximately 100 or 150 milliseconds.
Many currently known inflators are referred to as “dual-stage” inflators in that these devices contain two separate chambers that contain generant to be ignited separate from each other. Examples of these types of dual-stage inflators are disclosed in the followings patents (which patents are expressly incorporated herein by reference): U.S. Pat. No. 6,364,353; U.S. Pat. No. 6,142,515; U.S. Pat. No. 6,315,322; and U.S. Pat. No. 6,701,849. As explained in these patents, these dual-stage inflators are designed such that if the vehicle experiences a less-severe, less-dangerous crash, the initiator in the first chamber will be signaled and will be used to inflate the airbag. However, if a more serious crash is experienced such that the airbag needs to be inflated at a more rapid rate and/or to a greater peak pressure, then both the first chamber and the second chamber will be used to inflate the airbag.
Unfortunately, there are significant problems associated with currently known dual-stage inflators (such as the type disclosed in the above-referenced patents). Specific types of pyrotechnic dual-stage inflators are designed such that the second stage contains a supply of gas generant that is combusted to form a quantity of inflation gas. However, at the time that this combustion occurs in the second chamber, the internal pressure within the inflator has already been dissipated and brought back down to ambient (atmospheric) pressure (or near atmospheric pressure).
The combustion of the second initiator's gas generant at atmospheric pressure creates significant disadvantages. For example, such combustion at atmospheric pressure generally results in incomplete combustion/reaction of the gas generant. This incomplete combustion is undesirable in that it results in the formation of undesirable effluents or side-products. Vehicle manufacturers have determined that inflators producing such undesirable effluents may not be used in certain airbag applications. Likewise, in this situation, the late second chamber combustion will not produce gas rapidly enough to provide late event restraint of the occupant (which may be desirable in certain applications).
Accordingly, it would be an advancement in the art to produce a new type of dual-stage inflator that addresses these problems. More specifically, it would be an advancement to create a new dual-stage inflator that does not produce these undesirable effluents and may be used in all types of airbag applications. Such a device is disclosed herein.